This project consists of a three year program of research into the functioning of the voice source in speech and singing. The research can be divided into five areas, summarized as follows: (1) Our investigation of the influence on voice quality of acoustic interaction between the glottal source and the supraglottal vocal tract will be continued, using mathematical analysis supported by measurement of inverse-filtered oral air flow and the vocal fold contact area, as measured with the laryngograph version of the electroglottograph. Subjects used will include persons with a wide range of voice qualities, and include trained singers. (2) Measurements will be made of the air leakage during the "closed" phase of the glottal cycle during normal speech for subjects with a variety of voice qualities, in an effort to determine the relationship between such air flow and voice quality. (3) An algorithm for extracting a measure of vocal fold abduction from the vocal fold contact area waveform will be improved and tested. (4) A prototype "voice efficiency" meter will be constructed and tested that measures the ratio of effective radiated sound energy to aerodynamic energy absorbed by the laryngeal sound source. (5) The effect of transglottal pressure on vocal fold action will be measured through the use of forced variations in supraglottal pressure.